Backlight modules are basic components in liquid crystal displays. Currently, many types of backlight modules are used. For example, in a conventional side-lit backlight module, LED are disposed on both sides of the backlight module, and a light guide plate is provided in the display area of the LCD display, and thus the light emitted by the LED at two ends of the backlight module can be uniformly irradiated out of the backlight module via the light guide plate. In a direct-lit backlight module, a plurality of LED are provided in the display area of the LCD display directly, so the light guide is not required. However, the half-power angle of the radiation of each LED is about. +−0.60 degrees. Therefore, in the direct-lit backlight module, a distance must be kept above the LED so as to allow the light emitted by two neighboring LED to be partially overlapping. The above two types of backlight modules have advantages and disadvantages, respectively. The side-lit backlight module employing the light guide plate is usually heavier than the direct-lit backlight module. However, the LED in the side-lit backlight module are arranged less densely than those in the direct-lit backlight module. Due to its long light-mixing distance, the direct-lit backlight module is relatively thick and also requires an additional circuit board. Therefore, the cost of the overall structure of the direct-lit backlight module is higher.
US Patent Publication Nos. 2005/0007758A1, 2005/0140848A1 and U.S. Pat. No. 6,966,644 provide backlight modules with increased LED pitch. Firstly, US Patent Publication No. 2005/0007758A1 provides a strip-shaped light guide with a plurality of openings, and an LED is disposed at two ends of the light guide respectively. When the LED emit light, a plurality of openings of the light guide will radiate light to simulate a plurality of LED. Further, US Patent Publication No. 2005/0140548A1 provides a backlight module with a plurality of strip-shaped light guides, which is advantageous in that the brightness of the backlight module can be adjusted by individually driving the selected light guide. Moreover, U.S. Pat. No. 6,966,664 provides a light guiding strip, in which the light emitted by LED at two ends of the light guiding strip is concentratedly irradiated out from an arced surface of the light guiding strip, so as to form a linear and uniform light source.
Therefore, existing light guiding strip and backlight modules have these and other limitations. Accordingly, there is a need for a backlight module and double-sided planar light apparatus that solves these and other shortcomings of existing lighting devices.